"He did not reach out to anybody at the school", NYPD Chief of Detectives Robert Boyce said.

"It's unacceptable to ever lose a child to violence inside a school building", de Blasio said.

Boyce said that with Cedeno's mother stranded in hurricane-ravaged Puerto Rico, police were in contact with his older brother.

After leaving the classroom, 18-year-old Abel Cedeno handed the bloodied knife to a school counsellor he met in the hall, then went to an assistant principal's office and quietly waited for authorities to arrive, police said.

Students at a Bronx public school are returning a day after a stabbing left one teenager dead and another severely wounded. He has preliminarily been charged with one count of murder, two counts of of attempted murder, one count of manslaughter, one count of attempted manslaughter, two counts of assault, and two counts of criminal possession of a weapon. "He has a good heart", 18-year-old Asia Jones told DNAInfo.

The incident was said to have taken place in a building at 2024 Mohegan Avenue in the East Tremont section of the Bronx, New York City, at around 10:45 a.m EDT.

The New York City Department of Education - the largest school district in the country, with more than 1.1 million students in more than 1,800 schools - has had just one other homicide on school property in the last decade, in 2014 when a 14-year-old boy was killed in front of his Bronx middle school.

More than a dozen other students were in the classroom at the time of the stabbing, which occurred after McCree and Laboy were throwing broken pencils at Cedeno's head, police said.

In addition to the 15-year-old Matthew McRee, a 16-year-old, Ariane Laboy, was also stabbed during the confrontation at the Urban Assembly School for Wildlife Management. But it's the family of Matthew McCree that's paying the price.

Family members say McCree and Laboy relentlessly physically and verbally tormented their son since the start of the school year. She plans to pull her daughters out of school. "And they're crying, wondering what is going on, and the school didn't even call me". The school building does not have metal detectors, but the mayor said there would be random checks with metal detectors starting Thursday. "They're not safe because what happened happened in a class and they already got stabbed in class", said parent Yvette Santana.